Jan 2017 - Thermography

Accurate thermal monitoring during kiln heating-up phase

The starting process of a kiln is a critical phase that can cause serious damage to the shell and refractory bricks if not correctly managed; such management requires high-performance, real-time monitoring. It is a well-known phenomenon that during the firing-up phase, the kiln shell will heat up faster than the tires. Before reaching stabilization, these strong temperature gradients between kiln shell and colder tire rings can induce detrimental mechanical stresses to the kiln shell, resulting in shell deformation and ultimately increased rolling ovality, with possible consequences on the refractory lining such as crushing and radial abrasion. The continuous and real-time measurement of temperature, over the full length of the shell, and on tires and drive gear, is essential to ensure that the temperature differences are maintained below an acceptable threshold during the heating-up process.

The KILNSCAN thermal scanner provides the complete thermal map of the kiln with the sharpest spatial resolution and high thermal sensitivity, while the shell is slowly rotating during this startup phase. KILNSCAN detects hot spot at the earliest point, with a resolution better than the size of a single refractory brick. The thermal map of the shell is an indicator of the homogeneity of the kiln status, while hot spots reveal the wear of refractory bricks, cracked by a thermal shock.

In addition to continuous thermal monitoring, it is also of utmost importance to closely control the clearance between the tires and the kiln shell, so as to avoid permanent deformation, the tires shall not limit the expansion of the shell diameter. The tire silp function of KILNSCAN continuously monitors these clearance values, with alarm thresholds assigned to these parameters at each tire.

KILNSCAN also offers a unique feature that is definitely a valuable indicator of mechanical and thermal stresses in the shell and the tires, as well as load fluctuation and imbalances supported by each pier: the thermal warp computation. This function calculates the kiln thermo-mechanical distortion induced by temperature changes and non-uniformities over the shell. The evolution of the thermal warp figures provides information on the heating-up process evolution inside the kiln. Combined with the monitoring of the thermal map and with tire slip values and trends, these data warn of a potential risk during the operation and give the full picture to the plant maintenance staff in order to take corrective actions if necessary, such as slowing down the heating-up process for a better thermal distribution.

For more information about thermal warp, please read this article published in ZKG International magazine

Thermal monitoring during kiln heating-up

Kiln shell temperature measurement in shadow areas: local pyrometers or multiple scanners?

Shadow areas are zones where a single thermal scanner cannot measure the temperature of a kiln shell, because of obstacles in the line of sight of the scanner. For more information about shadow areas, visit the dedicated Frequently Asked Questions page on our website.

In order to monitor the temperature over the full length of the kiln shell, without leaving any blind spots, HGH can build up two solutions, depending on the configuration:

  • If there are a few small-size obstructions

In that case, several thermal spot sensors, called shadow pyrometers, are installed in front of the shadow areas, close to the shell. They are connected to the KILNSCAN receiver unit which operates as a data hub and merges temperature information from all sensors, to display the complete, seamless thermal map of the kiln shell.

Up to 8 shadow pyrometers can be connected to KILNSCAN receiver unit. Each pyrometer can be aligned in front of the kiln to monitor a spot equivalent to the size of a single refractory brick in shadowed or concealed areas.

  • If there are many obstructions or large-size masked areas
kiln masked with several posts and supports

As an example the above picture shows a typical complex configuration, where the line of sight of each scanner was obstructed by several posts and pillars. In comparable configurations, the best recommended thermal monitoring solution involves 2 or 3 scanner heads. At the plant where this picture was taken, 3 KILNSCAN scanners, each with a field of view of 140 °, were installed in order to display a thermal map with no dead zone. In such specific cases, wide-angle scanners are aligned with an overlap in their line of sights. The thermal image is then reconstructed by combining the data from these two or three scanners, eliminating shadows for a perfect full monitoring of the shell.

For another example of multiple KILNSCAN scanners installation to eliminate shadows, download our case study at the Xingyang plant .